Terpenes are a class of chemical components comprised of the fundamental building block of isoprene. Typically known for their olfactory stimulation, they are commonly used in the manufacture of chewing gum, candies and mints. They are also recognized for their diverse biological activity, often being touted as components which synergize with other endogenous and exogenous ligands. They are also recognized as entourage compounds, meaning that they increase the effects of ligands that bind to some receptors, while the compounds, themselves, have little affinity for the receptor.
Terpenes naturally are biosynthesized from units of isoprene, which can be linked to form linear chains or rings. In increasing length, the terpenes include hemiterpenes (single isoprenoid unit), monoterpenes (two units), sesquiterpenes (three units), diterpenes (four units), sesterterpenes (five units), triterpenes (six units), and so on. Terpenes are also known as terpenoids.
The fragrance of fruits and flowers is primarily due to aerosolized terpenes that are registered by the olfactory receptor neurons in the nose. In citrus fruits, the major aromatic compounds are limonene (LIM) and eucalyptol (EUC), which are both terpenes. The aromatic compounds of clove oil include eugenol and beta-caryophyllene (BCP), which are terpenes. The aromatic compounds of peppermint include LIM, menthone, and menthol, which are all terpenes.
The terpene composition of a sample, e.g., a plant, flower fruit, etc. can be analyzed with analytical tools, such as chromatography or mass spectrometry. Nonetheless, establishing the actual type and amount of terpene in a sample can be difficult because there may be hundreds of different terpenes in a sample, and terpenes with very different properties may differ by only the stereochemistry at a single carbon atom. See, for example, the well-known difference between R-(−)-carvone, which smells like spearmint, and S-(+)-cavone, which smells like caraway. Accordingly, determining the type and amount of each terpene in a sample will often require the use of complimentary analytical techniques, such as LC-MS and GC-MS.